1. Field of the Invention
This invention generally relates to methods and systems for processing a microelectronic topography and, more particularly, to methods and systems for depositing films upon microelectronic topographies using electroless plating processes and structures resulting therefrom.
2. Description of the Related Art
The following descriptions and examples are not admitted to be prior art by virtue of their inclusion within this section.
Electroless plating (also referred to herein as “electroless deposition”) is a process for depositing materials on a catalytic surface from an electrolyte solution without an external source of current. An advantage of an electroless plating process is that it can be selective, i.e., the material can be deposited only onto areas that demonstrate appropriate chemical properties. In particular, local deposition can be performed onto metals that exhibit an affinity to the material being deposited or onto areas pretreated or pre-activated, e.g., with a catalyst. The ratio of the deposition rate on the activated regions to the deposition rate at the non-activated regions is known as the “deposition process selectivity.” For many applications, it is important to provide a deposition of high selectivity. For instance, high deposition selectivity may be advantageous for the formation of metal features within integrated circuits, such as but not limited to contacts, vias, and interconnect lines.
Another important characteristic of an electroless plating process is producing a deposition profile which is commensurate with the fabrication specifications of the device. For instance, in some cases, it may be advantageous to have a film deposited with substantially uniform thickness. In cases in which a film is electrolessly deposited across a microelectronic topography, however, obtaining thickness uniformity may be difficult. In particular, some electroless plating techniques are susceptible to the “edge effect” in which portions of a film deposited near the edge of the wafer are thinner than the portions of the film deposited near the center of the wafer. Such an effect also hinders fabrication specifications for depositing films having greater thicknesses near the edge of the wafer as compared to near the center of the wafer.
As noted above, electroless plating may be used for the formation of metal features within integrated circuits. In some cases, electroless plating techniques may be particularly favorable for depositing materials into deep and/or narrow holes that cannot be uniformly covered by other deposition techniques, such as sputtering and evaporation, for example. In addition, electroless plating techniques may be advantageous for forming copper features, complementing the trend in the integrated circuit industry of employing copper metallization structures instead of aluminum, tungsten, silicides, or the like. In some microelectronic devices, a barrier layer may be arranged beneath and/or upon a metal feature to prevent elements within the metal feature from respectively diffusing to underlying and overlying layers of the topography. Such barrier layers may, in some embodiments, be formed by electroless plating processes. Although conventional barrier layers are generally sufficient to inhibit most elemental diffusion from a metal feature, some diffusion may still occur. For example, copper atoms are particularly notorious for being able to migrate through barrier layers. The migrated copper atoms can potentially be exposed to oxidation or moisture at the surface of the barrier layer or may tunnel through silicon materials disposed adjacent to the barrier layer, affecting the reliability of the device and, in some cases, causing the device to malfunction.
It would, therefore, be desirable to develop methods and systems for fabricating barrier layers which inhibit a greater degree of elemental diffusion from overlying and/or underlying metal features than provided by conventional barrier layers. In addition, it would be beneficial to develop systems and methods for electrolessly depositing films without incurring the edge effect.